Germanium and silicon additives to dual-layer electrophotographic plates

ABSTRACT

An electrophotographic photosensitive member comprises a layer containing selenium, tellurium and at least one of germanium and silicon as an additive and a layer containing selenium and at least one of germanium and silicon as an additive.

United States Patent Hanada et al.

[ Mar. 7, 1972 GERMANIUM AND SILICON ADDITIVES TO DUAL-LAYER ELECTROPHOTOGRAPHIC PLATES l-liroshi Hanada, Yokohama; Nobuo Kitaiima; Tatsuo Masaki, both of Tokyo, all of Japan Assignee: Cannon Kabushiki Kaisha, Tokyo, Japan Filed: Aug. 21, 1970 Appl. No.: 65,955

Inventors:

Foreign Application Priority Data Aug. 27, 1969 Japan ..44/67165 U.S.Cl ..96/l.5, 252/501, 117/215 Int. Cl. ..G03g 5/02 Field oiSearch ..252/50l;95/l.5

Primary Examiner-George F. Lesmes Assistant Examiner-John C. Cooper, 111 Attorney-Ward, McElhannon, Brooks & Fitzpatrick [57] ABSTRACT An electrophotographic photosensitive member comprises a layer containing selenium, tellurium and at least one of germanium and silicon as an additive and a layer containing selenium and at least one of germanium and silicon as an additive.

10 Claims, 1 Drawing Figure GERMANIUM AND SILICON ADDITIVES TO DUAL- LAYER ELECTROPHOTOGRAPHIC PLATES This invention relates to a photosensitive member for electrophotography. More particularly it relates to an improvement in a selenium photosensitive member and a panchromatic, durable and highly sensitive photosensitive member for electrophotography.

Heretofore, amorphous selenium has been widely used for electrophotographic photosensitive members. Amorphous selenium has advantageously appropriate electric resistance, high sensitivity and low fatigue effect. However, the photosensitive member mainly composed of amorphous selenium is liable to crystallize at a temperature higher than room temperature and furthermore, the crystallization is disadvantageously accelerated depending upon circumstance conditions such as temperature and light irradiation to which the photosensitive member is subsequently subjected. This crystallization decreases dark resistance of selenium and deteriorates the photosensitive member. The extended degree of crystallization results in short life of the photosensitive member. For example, volume resistivity of amorphous selenium at a dark place is higher than l' Q-cm., while that of crystallized selenium is about lO Q-cm, and therefore, crystallized selenium can not be used as photosensitive material as it is. It is necessary upon preparation of photosensitive members composed of amorphous photosensitive material such as amorphous selenium to maintain a temperature of a base on which vapor deposition of selenium is effected at a constant temperature. That is, the base is contacted with a beat bath kept at a constant temperature so as to prevent a temperature rise of the base during vapor deposition since a temperature rise results in starting of crystallization. In addition, control of vapor deposition temperature is also necessary so that a high degree of technique is requested in case of carrying out vapor deposition onto a drum-shaped base with rotating said drumshaped base. Accordingly, the manufacturing cost is expensrve.

A photosensitive member mainly composed of selenium has, in general, a low sensitivity to red light and lacks in panchromatic property which is essential to color image reproduction. Heretofore, this disadvantage has been eliminated by adding tellurium to selenium to form an amorphous selenium-tellurium alloy which is sensitive to red light region. The more the amount of tellurium added, the more panchromatic the alloy, as the result of the sensitivity to red light being elevated. However, the more the amount of tellurium in the alloy, the shorter the life of the photosensitive member. Therefore, the amount of tellurium is restricted to a range lower than percent by weight taking into consideration the durability of photosensitive member. Thus, the tellurium-selenium alloy photosensitive member is not practical.

According to another conventional improvement in selenium materials for panchromatic photosensitive members, a selenium layer is laid on an electroconductive base and further a this layer sensitive to red light such as a selenium-tellurium alloy layer is provided thereon. ln addition, a thin protecting layer composed of selenium-arsenic is laid on the thin layer sensitive to red light. However, such multilayer photosensitive member is not easily manufactured and the manufacturing cost is expensive.

When two photosensitive layers facing each different photosensitive region are laminated, the most effective structure for broadening the photosensitive region is that comprising a layer sensitive to short wavelength, i.e., blue light laminated on a layer sensitive to long wavelength, i.e., red light. On the contrary, it is usually known that when the order of lamination is opposite thereto, the photosensitive region can not be broadened. In a opposite lamination structure, all irradiation lights are apt to be absorbed at the upper layer.

In case that a stable selenium layer which is not easily crystallized is desired as a charge storing layer at the base side, it is inenitable to use such a opposite lamination structure in spite of the above mentioned defects. Thus, the resulting photosensitive member somewhat lacks in photosensitivity for blue light and can not be panchromatic, and further, deterioration of photosensitive property caused by crystallization is not solved.

Heretofore, there have not been any satisfactory photosensitive members, and development of photosensitive members of high sensitivity, panchromatic property, and high durability A still another object of this invention is to provide an elec-.

trophotographic photosensitive member having various sensitivity, panchromatic property and durability depending upon electrophotographic processes in which the photosensitive member is used.

Further objects and advantages of this invention will be apparent from the following description in conjunction with the drawing.

The drawing shows diagrammatically an enlarged cross-sectional view of an embodiment of a photosensitive member according to this invention.

According to the present invention, the photosensitive layer is prepared by laminating multilayers for the purpose of improving panchromatic property, durability and sensitivity of a selenium photosensitive member.

The electrophotographic photosensitive member according to this invention has a photoconductive layer composed of a layer l containing selenium, tellurium and at least one of germanium and silicon as an additive laminated with a layer ll.

order is opposite to that of a conventional photocensitive member. Such structure of photosensitive member of this invention can also eliminate the necessity of a protecting layer.

A selenium-tellurium alloy has a sensitive region at a long wavelength side, i.e., red light, but is easily deteriorated due to crystallization by addition of germanium and/or silicon and becomes unstable. Therefore, the selenium-tellurium alloy can not be used at a base side as an electric charge storing layer. A feature of this invention is that germanium and/or silicon is added to a selenium-tellurium alloy to produce a stable ternary or quaternary alloy and this stable ternary or quaternary alloy is used at a base side as an electric charge storing layer.

A layer to be laid on the above mentioned layer is composed of selenium, germanium and/or silicon alloy which has a photosensitive region at blue light, Le, a short wavelength side, and compensates the photosensitive region of the abovementioned selenium, tellurium, germanium and/or silicon alloy layer to give a panchromatic and highly sensitive photosensitive member. The alloy layer is stable and crystallization at the surface hardly occurs so that the alloy layer can be a protecting layer. Thus, any other protecting layer is not necessary and thereby a durable photosensitive member can be produced by using fewer layers than prior art. In other words, according to this invention, panchromatic property, durability and sensitivity of a selenium photosensitive member can be improved by using only two layers, and the selenium photosensitive member thus improved is very useful for color electrophotographic processes and can be easily produced at low cost since at most two layers are laminated.

Referring to the drawing, an electroconductive base I is made of brass, aluminum, copper and the like in a form of sheet, web, plate, cylinder, drum and other various desired forms with an optional thickness. Metallized paper and glass coated with a metallic film layer such as aluminum, copper iodide and the like may be employed. ln a particular case, the surface of the base may be coated with an insulating thin film layer. Further, in a more particular case, the base may be omitted.

A substantially glassy alloy layer 2 is composed of selenium, tellurium, germanium and/or silicon. Glassy alloy layer 2 may be optionally of a thickness ranging from about 10 to 300p, but the thickness preferably ranges from 20 to 80p. for commercial purpose. In general, a relatively thick layer such as thicker than 300p. has somewhat lower adhesiveness to the base so that a thickness ranging from 20 to 80a is preferred.

The amount of additive to the alloy may be widely varied. For example, tellurium may be contained in an amount ranging from percent (hereinafter percent is by weight unless otherwise specified) to 25 percent. With a content less than 5 percent, sensitivity to red light decreases somewhat while with a content over 25 percent there is disadvantageously given a high dark discharge. With respect to germanium and silicon, addition of a small amount thereof results in sufficient stabilization. Addition of a large amount thereof causes decrease in sensitivity so that an amount not higher than 5 percent is preferable, and more preferably it ranges from 0.001 to l percent for facilitating the manufacturing thereof.

A substantially glassy alloy layer 3 is composed mainly of selenium and an additive, that is, germanium and/or silicon and laminated onto layer 2, and the thickness of layer 3 is usually in a range from about 0.1 to 3p. The layer 3 in cooperation with the lower layer 2 gives the photosensitive member a panchromatic light response, i.e., sufficiently sensitive to a visible light up to a wave length of 4,000A. The contents of germanium and/or silicon is preferable somewhat higher than that in layer 2 and usually ranges from 0.1 to 5 percent to give a sufficiently stable alloy.

A most usual structure of photosensitive member according to this invention is that composed of a base and a photoconductive layer consisting of two layers laminated thereon.

An insulating layer 4 is not always necessary, but the layer 4 effectively protects the surface of the photosensitive layer and markedly improves the durability. Layer 4 is made of, for example, polyester film.

The resulting photosensitive member having the insulating layer 4 may be effectively used for an electrophotographic process as disclosed in Japanese Pat. Publication No. 43/23910, which is employed in Example 1 (infra.).

In the photosensitive member having an insulating layer as above, as far as either the base or the insulating layer is transparent to a radiation to which the photoconductive layer is sensitive, imagewise exposure can be carried out. In view of the gist of this invention, it is preferable that the'insulating layer is transparent.

According to another aspect of this invention, a switching layer is added to the photosensitive member to record the light image pattern as a resistance pattern for imparting a new function to the photosensitive member.

The photosensitive member according to this invention may be produced by various optional methods A representative method is a vapor deposition method. Some examples of vapor deposition method are shown below.

According to one method, a selenium, tellurium, germanium and/or silicon alloy, and a selenium, germanium and/or silicon alloy are subsequently applied to a base by vapor deposition in separate steps under vacuum ranging from to l0 mm. Hg. Or these two alloys are placed at different source portions in the same vacuum room and the two alloys are subsequently activated without breaking vacuum to form two layers.

Another method is a covapor deposition method comprising placing each component metal of the alloys under vacuum and controlling the temperature of each metal component source to form an alloy coating having a desired percentage of each component metal.

A further method is a flash vapor deposition method comprising placing a mixture of selenium, tellurium, germanium and silicon powders in a heating crucible at temperatures of about 400-600 C. in an appropriate amount and vaporizing the powder to deposite on a base.

ln the above-mentioned methods, the base is maintained at a temperature of about 50 to C. lf desired, a cooling apparatus such as a water cooling plate is used to maintain the base at a constant temperature. In general, when a vapor deposition is effected at about 280 C. at about 5X10' mm. Hg for about 1 hour, there is obtained a selenium, tellurium, germanium and/or silicon alloy layer of about 60p. in thickness.

The following examples are given for illustrating the present invention, but should not be construed as limitation to the present invention.

EXAMPLE 1 An aluminum plate of 1 mm. in thickness and 200 mm. 200 mm. was polished with a buff leather and sufficiently washed with trichlene vapor, and used as a base for a photosensitive member.

The aluminum plate was placed in close contact with a copper plate for controlling temperature kept at about 6070 C. in a vacuum room. Under the aluminum plate at a distance of about 25 cm. therefrom, there is provided a vesselhaving a cover with many small holes. In the vessel is placed an alloy of percent selenium, 15 percent tellurium, and 0.1 percent germanium. A shutter is provided between the base and the metal source.

Firstly, gas was evacuated at 180 C. for 30 minutes and the temperature of source was raised to 250 C. and the shutter was opened to effect vapor deposition for about 30 minutes and then theshutter was closed. As the result, an alloy layer of about 40p. in thickness was formed. A further vapor deposition was effected thereon for 4 minutes by using another metal source comprising an alloy of percent selenium, and 5 percent germanium at about 400 C. to form a layer of about 0.5 1. thick. In both cases above, the pressure was maintained at l0' l0 mm. Hg. during vapor deposition and the base was quenched to a room temperature after the shutter was closed. A polyester film of 12.5 ,1. thick was adhered to a surface of the photosensitive layer by using a small amount of epoxy resin of room temperature curing type to produce a photosensitive member. 7

The surface of the photosensitive member is given a negative charge of 2,000 v. by corona discharging of about 7,000 v. and then is given a corona charging of polarity opposite to the above simultaneously with exposing to a light image and finally the whole surface was subjected to uniform irradiation to produce electrostatic latent images.

This photosensitive member was panchromatic'to whole visible light and showed a sensitivity as high as about I lux. sec. This sensitivity is more than 10 times the sensitivity of conventional, so-called, Xerographic plates employing seleni- Very clear visible images of high resolving property were produced by developing the latent images with positively charged colored touer. When a liquid developer was used, a higher resolving power was shown.

For determining durability, the photosensitive member according to this invention was heated up to various temperatures such as 50, 60, 70 C. and the like to deteriorate it forcibly, and the results were compared with conventional selenium plates. As the results, it was found that the photosensitive member of this invention is as stable as'conventional selenium plates even if a surface insulating layer is not provided on the photosensitive member of this invention. Further, when a surface insulating layer was provided, the photosensitive member according to this invention. Further, when a surface insulating layer was provided, the photosensitive member according to this invention was hardly deteriorated. in addition, the photosensitive member having a surface insulating layer was mechanically stable and the characteristics thereof were hardly changed.

The comparison of characteristics is shown below.

EXAMPLE 2 A powder mixture of selenium, tellurium and germanium of above 99.99 percent in purity was sealed in a quartz ampul under vacuum of about mm. Hg. This ampul was heated at about 550 C. for 5 hours to melt the contents. During heating the ampul was rotated to form a homogeneous melt. Then, the ampul was dipped in water to quench a glassy alloy of selenium-tellariumgermanium thus obtained. These procedures were repeated to produce 10 glassy alloys having various contents, indicated as No.l-No.l0. The change of composition ratio was carried out by the change of mixing ratio of selenium, tellurium and germanium powders.

Contents (weight percent) The above glassy alloys were respectively applied to an aluminum base by vacuum vaporization to form an alloy layer of 60p thick. The vaporization condition is such that the vacuum is 10 to 10 mm. Hg, the temperature of aluminum base ranges from 60 to 78 C and the temperature of vaporization source is kept at 350 C.

By following the same procedure as in Example 1, an alloy having selenium 97 percent and germanium 3 percent was vapor-deposited upon these alloy layers to form an alloy layer of about 1p. thick. Thus, the photosensitive plates No.1 to No.10 were produced as corresponding to the glassy alloys No.1 to No.10. The photosensitivity and dark decay characteristics of these photosensitive plates were measured under the conditions as below shown.

Photosensitivity was determined by mounting a photosensitive plate on a rotary electrometer, charging positively, exposing to a 60 w. tungsten lamp and measuring an exposure amount (lux.sec.) required to decrease the potential to onetenth. This exposure amount was expressed as photosensitivity value. The exposure was started at 500 v. for each sample.

Dark decay was determined by charging the surface of a photosensitive plate to about +800 v. by using a corona charging device of +6 kv., allowing to stand at a dark place and measuring the time required to decrease the charge to half of the original charge, i.e., to 400 v. The reciprocal of said time is used as a dark decay value for facilitating the comparison with the photosensitivity value and the value of photosensitive plate No.1 is assumed as unit.

Photosensitivity values and dark decay values of the photosensitive plates No.1 to No.10 measured as above indicated are shown in the table below.

The above result shows that the photosensitive plates No.3 to No.7, i.e., the plates containing 2-25 percent tellurium are excellent in electrophotographic photosensitive characteristics.

EXAMPLE 3 in a manner similar to Example 2, selenium, tellurium and germanium powders were used to prepare the following 13 glassy alloys, No. l-No. 13.

Contents of component metal (wt. percent) The above mentio ed glassy alloy was deposited on an aluminum base plate under the same conditions as in Example 2 to form a film of 60p. in thickness by vacuum evaporation deposition. On the resulting alloy layer an alloy layer similar to Example 2 was formed. Thus, 13 kinds of photosensitive plate l-l 3 were produced. By using these photosensitive plates, photosensitivity and durability thereof were measured. The photosensitivity was measured in a manner similar to Example 2. The method for measuring durability is shown below. The photosensitive plate was uniformly positively charged by a corona discharger of +6 kv., and exposed to a light source of a 10 w. tungsten lamp at a distance of 30 cm. through a positive film for 2 seconds to produce latent images, followed by developing the image by a magnet brushing method to form visible images, which was then transferred to a paper. After the transferring, the photosensitive plate was cleaned and subjected to corona discharging in order to eliminate the remaining electric charge. The reproduction process was repeated in the same manner as above. Durability is represented by the Sample Photophotosensitive sensitivity plate value Durability nun-n.

The above result shows that the photosensitive plates 3-10 are particularly excellent, and the content of germanium ranging from about 0.001 to 5 percent is particularly excellent in electrophotographic characteristics. The same procedure repeated by using silicon instead of germanium gave a good result.

For example, when silicon was used in an amount of half the amount of germanium, the photosensitivity value and durability value were 80 percent of the values for germanium additive.

EXAMPLE 4 In a manner similar to Example 2, selenium, tellurium and germanium powders; 84.9 percent, 15 percent and 0.1 percent, respectively, were used to prepare a glassy alloy. This glassy alloy was uniformly deposited upon an aluminum base plate by vaporization to form a glassy alloy layer of 40p. thick in a manner similar to Example 1.

For further laminating an alloy layer upon this glassy alloy layer, the following 14 kinds of glassy alloys were prepared in a manner similar to Example 2.

Composition ratio (wt. percent) Selenium Germanium Glassy alloy Number:

Sample Photosenphotosensitive sitivity plate value Durability The following conclusion was induced from the above result regarding a secondary alloy layer. As the composition ratio of germanium is increased, the durability is increased while the photosensitivity is decreased. in the consideration of rate of such increase and decrease, it is recognized that the photosensitive plates No. 3-11, preferably No. 3-6, are excellent, i.e., the content of germanium ranging from 0.1 to 20 percent,

preferably from 0.1 to 5 percent, gives an excellent electrophotographic characteristics. in addition, it is recognized that the photosensitive plate No. 1 without germanium shows poor durability.

By using equal amounts of germanium and silicon instead of germanium in the above example, a secondary alloy layer was prepared without changing the component ratio. For example, in the glassy alloy No. 3 in the previously shown table, the percents of germanium and silicon were 0.05 percent, respectively, and the sum of them was still 0.1 percent; in the glassy alloy No. 8, the percents of germanium and silicon were 5 percent respectively and the sum of them was still 10 percent. By using these glassy alloys, a secondary alloy layer was formed to produce photosensitive plate No. l-l4 shown in the following table. The resulting photosensitivity and durability of these photosensitive plates are shown in the following table.

What is claimed is:

I. An electrophotographic photosensitive member which comprises a first photoconductive layer consisting essentially of selenium, tellurium and from about 0.001 to about 5 weight-percent of an additive selected from the group consisting of germanium and silicon and a second photoconductive layer consisting essentially of selenium and from about 0.1 to about 5 weight-percent of an additive selected from the group consisting of germanium and silicon, said second photoconductive layer having a photoconductive response different from that of said first photoconductive layer.

2. An electrophotographic photosensitive member according to claim 1 in which the first layer is between 20 and p. in thickness.

3. An electrophotographic photosensitive member according to claim 1 in which the content of tellurium in the first layer ranges from 5 to 25 weight-percent.

4.- An electrophotographic photosensitive member according to claim 1 in which the content of the additive in the first layer ranges from 0.001 to l weight-percent.

5. An electrophotographic photosensitive member according to claim 1 in which the second layer is between 0.1 and 3p. in thickness.

6. An electrophotographic photosensitive member according to claim 1 wherein the content by weight-percent of the additive in the second layer is larger than that of the additive in the first layer.

7. .An electrophotographic photosensitive member which comprises a base layer, a first photoconductive layer laminated on said base layer consisting essentially of selenium, tellurium and from about 0.001 to about 5 weight-percent of an additive selected from the group consisting of germanium and silicon and a second photoconductive layer laminated on said first photoconductive layer consisting essentially of selenium and from about 0.1 to about 5 weight-percent of an additive selected from the group consisting of germanium and silicon, said second photoconductive layer having a photoconductive response different from that of said first photoconductive layer.

8. An electrophotographic photosensitive member according to claim 7 in which the base is electroconductive.

9. An electrophotographic photosensitive member according to claim 7 in which the base is insulating,

10. An electrophotographic plrotd s nsitive member accordmums 0165 

2. An electrophotographic photosensitive member according to claim 1 in which the first layer is between 20 and 80 Mu in thickness.
 3. An electrophotographic photosensitive member according to claim 1 in which the content of tellurium in the first layer ranges from 5 to 25 weight-percent.
 4. An electrophotographic photosensitive member according to claim 1 in which the content of the additive in the first layer ranges from 0.001 to 1 weight-percent.
 5. An electrophotographic photosensitive member according to claim 1 in which the second layer is between 0.1 and 3 Mu in thickness.
 6. An electrophotographic photosensitive member according to claim 1 wherein the content by weight-percent of the additive in the second layer is larger than that of the additive in the first layer.
 7. An electrophotographic photosensitive member which comprises a base layer, a first photoconductive layer laminated on said base layer consisting essentially of selenium, tellurium and from about 0.001 to about 5 weight-percent of an additive selected from the group consisting of germanium and silicon and a second photoconductive layer laminaTed on said first photoconductive layer consisting essentially of selenium and from about 0.1 to about 5 weight-percent of an additive selected from the group consisting of germanium and silicon, said second photoconductive layer having a photoconductive response different from that of said first photoconductive layer.
 8. An electrophotographic photosensitive member according to claim 7 in which the base is electroconductive.
 9. An electrophotographic photosensitive member according to claim 7 in which the base is insulating.
 10. An electrophotographic photosensitive member according to claim 9 in which a transparent insulating layer is laminated on the second photoconductive layer. 